For the most updated documentation, consult the iDRAC9 documentation support portal. Some particularly helpful links are highlighted below. Each one relates to how Dell implements Secure Boot customization.
- Signing UEFI images for Secure Boot feature in the 14th generation and later Dell EMC PowerEdge servers
- iDRAC RACADM CLI Guide (look to page 35 for "bioscert"
- BIOS/UEFI F2 Config Secure Boot Policy Brief
Dell EMC has also published several helpful videos regarding navigating Secure Boot options.